ALASKAN GLACIER STUDIES
system of through valleys was different from the present, and it is possible that the breadth and flatness of the high divides of the present day are in large part the result of the flow of ice across the divides from which the glaciers now descend in two directions.
Although we had not visited the Fourth Glacier before 1909, we are convinced from its present condition that it has not yet been subjected to a forward thrust as a result of the influence of the 1899 earthquakes. Had it been, its surface would have necessarily retained some evidence of the former breaking, for it is inconceivable that ablation could have so reduced the irregularities as to have made such a smooth surface as the present. Four years of ablation on Variegated Glacier have made it possible to again travel over the surface, but has still left the surface so rough that one must use care in such traveling. Granting even six or seven years of ablation, which is the maximum which could possibly be inferred, a badly-broken ice surface could not be reduced to such smoothness as was observed on the Fourth Glacier. Further proof that this glacier has not been
subjected to a spasmodic advance of considerable proportions is found in the fact that the glacier front and margins are fringed by extensive areas from which the glacier has receded. With recent advance under earthquake impulse evidence of the reverse condition should bepresent (PI. LXXXVin). We feel confident, therefore, that Fourth Glacier has not yet responded to the influence of the earthquake shocks. It was not visited in 1910 but its stream delta seemed unchanged at that
time. Prospectors used it as a highway in 1898 and 1899 and in several years since, and we have heard no report of its being crevassed and impassable during the last ten years from these men, some of whose sledges and snowshoes we found on the glacier surface in 1909.
It is possible that the Fourth Glacier may never advance under the earthquake impulse, provided its supply ground did not receive extensive avalanches in 1899, but about this we cannot be certain. However, from such indications as we have concerning the conditions under which Fourth Glacier is supplied, we infer that it will ultimately respond to the impulse. It is, therefore, one of the glaciers which should be examined in future expeditions to the Yakutat Bay region. Two photographic stations were established in 1909, from which future observations may be made, and a sketch map of the ice front and its surroundings was made (Fig. 16). This, however, should be understood to be merely a record of general forms, the contours not being determined carefully, and all being located with respect to a single aneroid determination of altitude.
FIG. 16. SKETCH MAP 07 FOURTH GLAOIEH IN 1909.